Coleopteran Carnage

by Pavan Kaushik – The sky was red in the west and black in the east. The world seemed to be illuminated from an invisible, omnidirectional soft light. The temperate souls might remark, “Overcast, gloomy weather!” We call it the onset of monsoon. I was half naked, “dressed” up to get drenched. While I waited for the sky to pour, I saw a bright red blob amidst the grays. On closer inspection, I realized that it was the classical red polka dotted ladybird on a bamboo stem. Except, it was big, the largest I had ever seen. It was not a case of “mine is X cm longer”, this was three fold larger than the usual, making all comparisons look pale. I borrowed a camera from a passerby and documented it with a “scale”.

I was about to carry on with my tropical pleasures, when I noticed that the gracefully growing bamboo was covered with a grey haze. There were tiny grey things with white bums moving around. Aphids of varying sizes, shapes and colors. They completely covered the bamboo, sucking the life out of it. I lamented, “You shall die before you bloom”.

A couple of days later, I was going past the bamboo bush hoping to see the ladybug again (probably I didn’t appreciate probability enough). But what I saw instead was a dash of bright yellow and black. Thorny, vicious caterpillars, bashing each other with their abdomens, eating everything that came in their way. They looked scary and one can see the destruction(cleansing) left in their wake. The video shows in sequence an uninfested bamboo, infestation, the carnage, and the remains. In a matter of a few days, the entire bamboo was naked barring the remnants of the carnage, the moults and those who did not make it. After googling, I confirmed that it was the giant bamboo ladybird (Synonycha grandis). It is one of the largest ladybugs in the world and the largest in India. Their voracious nature hasn’t gone unnoticed and they have been successfully used in pest management. Who knew, that the pretty ladybug had a gory past?

Amidst all the superlatives, one cannot fail to observe that the beetles find the infested bamboo amidst the hundreds of bamboos on campus. After this incident, every time I pass by any bamboo bush, I look for aphids. But, it has been over 2 years now and I have never seen this phenomenon again anywhere. Assuming that I am a reliable observer, this makes the case that aphid infested bamboos are uncommon if not rare. Then how do these beetles find their food? It is likely that there is an olfactory component involved as vision is insufficient considering insect vision and the sparseness of the object of interest. Are the beetles eavesdropping or is the bamboo is sending out help signals? What decides the ideal time for the ladybird to lay eggs? If they are early, the aphid population isn’t large enough. If they are too late, aphids fly away. How are the three populations maintained, since each of them work at a different timescales, the bamboo grows in the order of months, while the aphids grow in weeks and the beetle in days? If you look at the positioning, the beetle larvae are like the teeth of a decorticator (bark removing device), feeding on the “bark” of the bamboo. If the larvae were positioned randomly, would they be sub-optimal? If you notice the remnants of the carnage, it is speckled with first and second instar aphids. Did the larvae ignore them as small fish or did the tiny aphids just sneak away? One can answer many questions regarding optimal foraging as this is a neat system where the larvae are in a-Ph[i]D heaven, therefore, there is no transit or search time. All that matters is food handling time and the decisions the larvae make on which aphid to eat.

Phenomenon like these run a common theme. There is no free lunch and if there is, it will be plagued by competition. The same reasons that differentiate tropical and temperate lives.